To achieve the desired confocal depth discrimination so that the image of the image field located in a predetermined depth of the specimen to be examined can be generated, laser scanning microscopy uses a diaphragm that shuts out undesirable light from the specimen.
It is also known that to achieve confocal depth discrimination in the wide field or on partial illumination of the image field (e.g., line illumination), it is possible to structure the illumination (or to modulate the intensity). By means of a phase shift of the structured illumination, a depth-discriminated optical section can subsequently be calculated and thus the desired image of the object can be generated. As, for example, described by M. A. A. Neil et al. in “Method of obtaining optical sectioning by using structured light in a conventional microscope,” Optics Letters 22 (24), 1997, pp. 1905-1907,this can be achieved with three phase images at 0°, 120° and 240°.
To structure the illumination, it has been proposed to use gratings in the bundle of illuminating rays or the interference of coherent partial beams or diffractive optical elements. A disadvantage is the inherent inflexibility of these techniques and the increased labor requirement and expenditure of time since a change of the lens of the laser microscope generally also requires a change in structuring. Thus, as a rule, a different grating has to be used, the interference of the coherent partial beams has to be changed, or a different diffractive optical element has to be used.